Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Figure 4.17 Wear rate vs carbon nanotube volume content for
Cu/MWNT nanocomposites at different applied loads.
Reproduced with permission from [45]. Copyright Ó (2003)
Elsevier.
4.4 Wearj123
The CNTs were coated with electrodeless nickel to ensure good wetting between the
copper matrix and nanotubes. Pores are formed in such nanocomposites processed
by the PM route, ranging from 2.56% for composite filled with 4% CNT to 4.92% for
sample with 16 vol% CNT. Figure 4.17 shows the variation of wear rate with nanotube
content for the Cu/MWNT nanocomposites subjected to the pin-on-disk test at
different applied loads. For applied loads below 30 N, the wear rate generally
decreases with increasing nanotube content. At 50 N, the wear rate first decreases
with increasing filler content up to 12 vol%, and then increases as the nanotube
content reaches 16 vol%. This can be attributed to the high porosity content (4.92%)
in the Cu/16 vol% MWNT nanocomposite. Thus, the wear rate of copper nanocomposites
depends greatly on the microstructure and applied load under dry sliding
conditions.
Dong et al. also studied the sliding wear behavior of Cu/CNT nanocomposites
prepared by PM ball milling and sintering (850 C) [46]. They also fabricated CF/Cu
composites in the same way for the purpose of comparison. This is because the Cu/
CF composites are widely used for electric brushes and electronic component
pedestals applications. They reported that the Cu/CNTnanocomposites exhibit lower
friction coefficient and wear loss than those of Cu/CF composites due to the much
higher strength of nanotubes. The optimum nanotube content in the nanocomposites
for tribological application is 12–15 vol%.
For Cu/MWNT nanocomposites prepared by molecular level mixing and SPS
consolidation [Chap. 2, Ref. 87], CNTs are found to disperse homogeneously within
the copper matrix; thus MWNT additions enhance the hardness of copper. Consequently,
the wear resistance of copper is considerably improved by adding CNTs
(Figure 4.18(a) and (b)). Compared with the copper nanocomposites fabricated by PM
processing and slid at 30 N (Figure 4.17), Cu/MWNT nanocomposites densified by
SPS exhibit much lower wear rates as expected.